Hydrogen is nowadays produced by means of PEM electrolysis, as an example. A component of a PEM electrolyzer is a polymer membrane which is permeable to protons (proton exchange membrane), both sides of which being in contact with porous platinum electrodes (anode and cathode). An external voltage is applied to them and water is supplied to the anode side of the electrolyzer. The catalytic action of the platinum breaks down the water on the anode side. Oxygen, free electrons and positively charged hydrogen ions, H+, are thus produced. The hydrogen ions H+ diffuse through the proton exchange membrane to the cathode side where they combine with electrons from the external circuit to form hydrogen molecules, H2.
Splitting water into hydrogen and oxygen by electrolysis opens up the possibility of storing surplus electricity in the form of hydrogen or oxygen. Following the reaction, most of the electrical energy that has been introduced is recovered in the chemical energy of the hydrogen and oxygen products. However, in addition to the hydrogen and oxygen products, losses also occur in the electrolysis process that are incurred in the form of heat of reaction. In this connection, it should be noted that during the electrolysis, a considerable amount of electrical energy is converted into heat energy or waste heat, which at the present time is for the most part dissipated and not put to use. This is largely because the amount of waste heat varies widely from a relatively low temperature of approximately 30° C. up to 80° C.
DE 10 2005 011 316 A1, as an example, discloses that the heat of the hydrogen and oxygen streams produced in the electrolyzer is given up to preheat the water required for the electrolysis.